A research team compares two model exchange surfaces. The relative diffusion value is calculated using:
relative diffusion value=surface area×concentration differencemembrane thickness \text{relative diffusion value}=\frac{\text{surface area}\times\text{concentration difference}}{\text{membrane thickness}} relative diffusion value=membrane thicknesssurface area×concentration difference| Model exchange surface | Surface area (mm2^22) | Concentration difference (mmol dm−3^{-3}−3) | Membrane thickness (mm) |
|---|---|---|---|
| A | 40 | 6.0 | 0.20 |
| B | 60 | 4.0 | 0.30 |
The team redesigns surface B. Its surface area is doubled and its membrane thickness is halved. The concentration difference stays the same.
Calculate the relative diffusion value for each model exchange surface before the redesign.
Calculate how many times greater the relative diffusion value of redesigned surface B is than that of surface A.
102 exam-style questions on Edexcel GCSE Biology 8.1 Exchange surfaces and diffusion, covering 8.1.1 Introduction to exchange and transport, 8.1.2 Alveoli adapted for gas exchange, 8.1.3 Factors affecting rate of diffusion, and 8.1.4 Rate of diffusion using Fick's law. Each one has a worked solution and a mark scheme showing where the marks go.